1. Field of the Invention
The invention concerns a heating element, preferably a radiant heating body for glass ceramic hobs.
2. Discussion of the Prior Art
Heating elements of the above-indicated kind are known per se. Thus DE 33 15 438 A1 discloses such a heating element which is formed from an insulating carrier and a receiving dish and which, for heating glass ceramic cooking hob areas, is arranged beneath the glass ceramic plate. The heating element has three heating conductors of which two are arranged in series one behind the other, while the third heating conductor extends parallel to them. That arrangement is intended to achieve an improved relationship between heating conductor length and heating conductor output power. A particularly advantageous use arises in the case of radiant heating bodies in order to use a seven-stage switch.
A seven-stage circuit for hot plates, which is also known from a practical context, is disclosed in German patent specification No. 12 39 034. In that arrangement a respective end of two heating conductors or heating spirals is connected to an output terminal of the switch. The remaining four ends of the heating conductors are brought together in pairs and also connected to a respective output terminal. A graduation in terms of output power is achieved by virtue of connecting the output terminal of the switch to the two pole terminals of a dc or ac network system, in a predetermined switching sequence. That patent specification is based on the realisation that, while retaining the known seven-stage switch arrangement, it is not possible to provide between switching stages II and I a further switching position in which the third output terminal is not connected to one of the two pole terminals. It was therefore necessary to look for a way of completely avoiding that pole change without in that respect anything changing in terms of the series connection of the three heating conductors in the first switching position of the series circuit of the second and third heating conductors in switching position II. Therefore, in accordance with patent specification No. 12 39 034, the inevitable pole change was effected on the one hand in relation to switching positions II and IV and on the other hand in relation to switching positions IV and II. More specifically, in the former case the neutral switching position III is between the pole change, while in the second case that involves the two neutral positions I and OFF.
Those heating elements in the state of the art have been found to suffer from the disadvantage of the excessively great power graduation effect and the temperature distribution, which is at least in part not an optimum one, in regard to seven-stage heating with a seven-stage switch. It was further realised that the energy regulator cycles the output power in respect of time. As a result in the low output power stages the energy regulator has excessively long OFF-times.